GB2352110A

GB2352110A - Plastic optical fibre cables in a telecommunication exchange

Info

Publication number: GB2352110A
Application number: GB9916382A
Authority: GB
Inventors: Demetri Kalymnoius; John King
Original assignee: Taiko Denki Co Ltd
Current assignee: Taiko Denki Co Ltd
Priority date: 1999-07-14
Filing date: 1999-07-14
Publication date: 2001-01-17
Also published as: WO2001006289A8; WO2001006289A1; GB9916382D0

Abstract

A telecommunications exchange comprising a plurality of multiplexers 12,14,16,18 wherein at least some of the multiplexers 12,14,16,18 are connected using plastic optical fibre (POF) cables 26. Also disclosed is a U-link connector having at least one generally U-shaped groove adapted to receive a length of POF cable.

Description

2352110 M&C Folio No P50673GB Improvements in and relating to Exchanges

The invention relates to telecommunications exchanges and U-Iink connectors for use in such exchanges.

The invention is particularly applicable in Synchronous Digital Hierarchy (SDH) exchanges which comprise a number of multiplexers and demultiplexers connected together using Digital Distribution Frames (DDFs). In such an exchange telephone signals carried by standard twisted pairs are connected to a glass fibre by means of a series of multiplexers and de-multiplexers. It is known to use coaxial cables to connect the multiplexers, but this is relatively expensive and the weight and size of the coaxial cables required can cause cable management difficulties. Furthermore, interference problems can arise from the use of such coaxial cables. The interference problems are two-fold: susceptibility to external interference due to a less than 100% braid coverage and crosstalk due to parallel runs of cable in the cable management system around the DDFs.

The invention provides an improved telecommunications exchange interconnect system and a U-1ink connector as set out in the accompanying claims.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure I shows a simplified representation of the transmission part of a Synchronous Digital Hierarchy (SDH) exchange; Figure 2 is a simplified drawing of a Digital Distribution Frame (DDF) used in the exchange of Figure 1; Figure 3 is a schematic representation of four outlets in a mounting block in the DDF of Figure 2; 1 M&C Folio No P50673GB 2 Figure 4 shows one half of a U-Iink connector for use in the exchange of Figure 1; Figure 5 shows the other side of the half of the U-Iink connector of Figure 4; 5 Figure 6 shows the complete U-Iink connector; and Figure 7 shows the rear of the complete U-Iink connector.

Figure 1 shows the transmission part of an SDH exchange, comprising a digital Krone DDF 4 (being a known type of DDF suitable for use with standard telephone line twisted pairs), three further DDFs 6, 8 and 10, and four multiplexers 12, 14, 16 and 18.

The first multiplexer 12 is a 64kB/s to 2MB/s multiplexer. The second multiplexer 14 is a 2MB/s to 8MB/s multiplexer. The third multiplexer 16 is a 8MB/s to 32MB/s multiplexer. The fourth multiplexer 18 is a 32MB/s to 155MB/s multiplexer.

Signals enter the exchange 2 via a plurality of twisted pairs 20, and leave the exchange via a glass fibre 22. Signals are transmitted from the Krone DDF 4 to the first multiplexer 12 by a plurality of twisted pairs 24.

The remaining connections between multiplexers and DDFs in the exchange 2 of Figure I have hitherto been made using coaxial cables. However, in this embodiment of the invention these connections are made using plastic optical fibre (POF) cables 26.

Suitable POF cables include those supplied by Mitsubishi Rayon Co. Limited of Japan, for example those sold under the reference number GHNF 4001.

The POF cables 26 provide a number of advantages. The POF cables 26 are cheaper and also allow improved cable management as a result of their smaller diameter and lighter weight when compared with coaxial cable. The characteristics of POF also eliminate electrical problems such as electromagnetic interference and cross-talk.

M&C Folio No P50673GB 3 In a farther embodiment of the invention the glass fibre 22 can be replaced by a POF cable for short runs, for example for connection between different floors in the same building. For long distances, it is still necessary to use silica fibre.

Figure 2 shows a Digital Distribution Frame (DDF) which comprises a metal frame 28 which houses a plurality of injection moulded plastic mounting blocks 30, each of which provides a number of outlets 32. The outlets 32 are arranged in groups of four as shown in Figure 3.

Referring to Figure 3, there is shown a group of four outlets 34, 36, 38 and 40. The first and second outlets 34 and 36 are connected by a U-1ink, illustrated schematically as 42. Similarly, the third and fourth outlets 38 and 40 are connected by a U-1ink, illustrated schematically as 44.

In the example of Figure 3, the first outlet receives a signal from the first multiplexer 12, which is passed via the second outlet 36 to the second multiplexer 14. The third and fourth outlets 38 and 40 relate to the receive part of the exchange (not shown in Figure 1). The fourth outlet 40 receives a signal from an 8-2 NM/s de-multiplexer (not shoVM), and the third outlet 38 passes this signal to a 2 MB/s - 64kB/s demultiplexer (not shown). The four outlets of Figure 4 thus form a dual simplex system, which allows duplex communication. The four outlets 32 of Figure 3 would, for example, handle the transmitted and received signals in a single telephone circuit.

Figures 4 to 7 show a U-1ink connector, which can be used with a short length of plastic optical fibre (POF) cable to form the U-1inks 42 and 44 shown in Figure 3.

Referring to Figure 4, there is shown one half 50 of a U-1ink connector 52, which is shown in assembled form in Figures 6 and 7. The U-1ink connector 52 is formed from two identical halves 50 and a rear clip 54, all components being formed from injection moulded plastic, although other suitable materials may be used.

M&C Folio No P50673GB 4 Each half 50 comprises a generally semi-circular groove 56 adapted to receive a POF cable (not shown). Five domes 58 are provided within the groove 56. When the two halves 50 are connected together the domes 50 indent the surface of the POF cable, without causing damage, in order to grip the POF cable more securely. The two ends of the groove 56 comprise straight portions which are perpendicular to the front surface of the connector 52. This ensures that the cable axis is truly orthogonal to the mating face to minimise angular misalignment with the fibres in the connector block.

The two halves 50 are connected together by means of a locating projection 60 and corresponding locating recess 62, together with a flexible arm 64 provided with a detent portion 66 which engages within a recess 68 in the other half of the U-Iink connector 52.

The rear clip 54 is provided with detent portions (not shown) which engage within a groove 70 formed along the rear of each half 50. The rear clip 54 is provided with a large flat rear surface 72, to which a label may be attached to identify the circuit to which the U-Iink connector 52 corresponds. The rear clip 54 may also be colour coded to indicate which multiplexer it is associated with.

The U-Iink connector 52 is designed to form a connection between two outlets 32 formed in a mounting block 30 (see Figure 2). To this end, each half 50 is provided with a flexible arrn 74 having a detent portion 76 adapted to releasably engage within a corresponding recess (not shown) in the mounting block 30.

Furthermore, part-circular projections 78 are provided on the front surface 80 of each half 50, and these are intended to be received by a circular groove formed in the mounting block 30 in order to align the POF cables correctly. The projections 78 are arranged concentrically with the POF cable, and are also dimensioned to ensure that an appropriate small gap is left at the ends of the connected POF cable when the U-Iink connector 52 is connected to,the mounting block 30.

M&C Folio No P50673GB 5 Each half 50 is provided with two such projections 78 which are arranged so that when the U-Iink connector 52 is assembled a gap 82 is provided between the projections 78 to allow a blade to trim the POF cable flush with the front surface 80 once the POF cable is secured within the U-Iink connector 52. 5 Returning to Figures 2 and 3, the U-Iink connector 52 can be used to connect corresponding pairs of outlets 32. The advantage of such removable U-Iink connectors 52 is that if a multiplexer fails or requires routine maintenance, the appropriate U-Iink connectors 52 can be removed from the mounting block 30 in order to allow other 10 temporary connections to be made until the multiplexer is again available for use.

M&C Folio No P50673GB 6

Claims

CLAIMS:

1. A telecommunications exchange interconnect system comprising a plurality of multiplexers, wherein at least some of the multiplexers are connected using plastic 5 optical fibre (POF) cables.

2. A telecommunications exchange interconnect system as claimed in claim 1, which is a Synchronous Digital Hierarchy (SDH) exchange.

3. A telecommunications exchange interconnect system as claimed in claim I or 2, wherein said POF cables are used for connecting multiplexers for multiplexing signals from about 64kB/s to about 155MB/s.

4. A telecommunications exchange interconnect system as claimed in any preceding claim, wherein the exchange further comprises a plurality of demultiplexers, at least some of which are connected using POF cables.

5. A U-1ink connector for use in a telecommunications exchange, said U1ink connector comprising at least one generally U-shaped groove adapted to receive a length of plastic optical fibre (POF) cable.

6. A U-1ink connector as claimed in claim 5 which comprises two parts which are securable to each other in order to grip said length of POF cable therebetween.

7. A U-link connector as claimed in claim 5, wherein said two parts are substantially identical to each other.

8. A U-1ink connector as claimed in any one of claims 5 to 7, which further comprises a rear clip, securable to the rear of the connector, and provided with a flat surface for displaying a label.

M&C Folio No P50673GB 7

9. A telecommunications exchange interconnect system as claimed in any one of claims I to 4 comprising a U-Iink connector as claimed in any one of claims 5 to 8.

10. A telecommunications exchange interconnect system substantially as 5 hereinbefore described with reference to Figures I to 3.

11. A U-Iink connector substantially as hereiribefore described with reference to Figures 4 to 7.